Slide rule with improved calculating capacity

ABSTRACT

A slide rule with improved calculating capacity has, in addition to the A, B, C, D and related scales, a folded square scale BF whose origin pi coincides with the left-hand indices 1 of the previously mentioned scales and which runs to the value 36 on the slider. The balance of the length of the slider is provided with a centesimal trigonometric scale.

United States Paten 91 [111 3,782,626 Hondrea Jan; 1, 1974 SLIDE RULEWITH IMPROVED Rule, Keuffel & Esser Co., N.Y., i924.

CALCULATING CAPACITY Inventor: Iosif Hondrea, Rimisoara, Romania [73]Assignee: Iprofil Technolemn"-Industria Produselor Finite Din LemnTimisoara, Noembrie, Romania [22] Filed: June 21, 1971 [21] Appl. No;154,745

[52] US. Cl, 235/70 R, 235/70 C [51] Int. Cl 606g 1/02 [58] Field ofSearch 235/70 A, 70 C, 70 R [56] References Cited 0 UNITED STATESPATENTS I 2,500,460 3/1950 Hunt 235/70 R 1,168,059 l/l9i6 Cuntz 235/70 ROTHER PUBLICATIONS Directions for the Use of Roylance Electrical SlideIBM Technical Disclosure Bulletin, Vol. 1 1, No. l l, p. 1563, 1564,April, 1969.

Primary ExaminerRichard B. Wilkinson Assistant Examiner.lohn F. GonzalesAtt0rneyKarl F. Ross [57] ABSTRACT A slide rule with improvedcalculating capacity has, in addition to the A, B, C, D and relatedscales, a folded square scale BF whose origin 11- coincides with thelefthand indices 1 of the previously mentioned scales and which runs tothe value 36 on the slider. The balance of the length of the slider is'provided with a centesimal trigonometric scale.

' 8 Claims, 3 Drawing Figures M n f PATENTEU AH r914 35m 1 OF 2 m v w uPATENTEU 1 4 SHEET 2 OF 2 m 2 3 3 2 on 2 SLIDE RULE WITH-IMPROVEDCALCULATING CAPACITY FIELD OF THE INVENTION My present invention relatesto a general purpose calculating instrument and, more particularly, to aslide rule with improved calculating capacity and facility of operation.

BACKGROUND OF THE INVENTION Slide rules have gained increasingprominence as a calculating means because of their ease in handling,carrying facility and versatility. In general, the most commonly usedslide rules are circular and linear rules having a rule body marked withcertain scales, a slide shiftable within a groove or channel of the rulebody and marked with other cooperating scales, and a cursor or slideshiftable along the body, of the rule and being transparent over atleast a window to permitthe viewing of the scales therebeneath. Areticle or hairline is provided ,on' the window, with or without amagnifying lens, to permit selection of a value for manipulating on thescale below.

V In practice, the slide rule may have a length of, say, 125 mm(pocket'size), a length of 250 mm (normal size) or, say, 1,000 mm(extra-long) with increasing accuracy and precision. A slide rule isfrequently capable of calculations with three or four significantfigures, the variety ofcalculations being limited only by the number ofscales available. It is not uncommon, therefore, for the slide rule tobe provided with scales necessary for ordinary or usual calculations,with scales required for calculations which arise infrequently but aredesirable for special purposes (special-purpose scales), and withindices or markings representing relationships, constants and valueswhich arise frequently in specialized or general calculation. Typical ofsuch special indices or markings are those at the magnitude e 2.718 andcorresponding to the natural logarithm base, 11' or multiples thereof,etc.

The slide rule may have its versatility increased by adding scales orspecial markings as already noted, by increased fineness of thesubdivision of the scale, and by the provision of scales of extralength. The latter case has the disadvantage that, with increasinglength, the slide rule may become unwieldy and difficult to manipulatepA conventional general purpose slide rule may have,

. along the face of the longitudinally extending slide,a basiclogarithmically divided base-valve scale C repreprovided alogarithmically'divided square A scale representing the value X where Xis selected by means of the hairline on the D scale, and a squaringscale B subdivided identically to scale A is formed on the slide tocooperate with scale A. These are the basic scales for multiplication,division, squaring, extraction of square roots and for simple or complexratio solutions. Apart from these basic scales, scales of less thangeneral purpose, but greater utility than the highly specialized scalesmentioned earlier, are usually provided. These scales are designed toassist in calculations affecting a large portion of the scientific,mathematical and engineering community. These scales include alogarithmically devided K (cube) scale representing the value X when Xis selected by the hairline of the cursor along either the C or D scale.Other scales of intermediate utility are logarithmically dividedreciprocal scales CI and/or DI, respectively, representing the valuesl/X, where X is selected by moving the hairline to the appropriate valueon the C or D scale respectively, the reciprocal square scales Al andBI, representing the values of l/X and other scales corresponding tol0/X, l00/X etc. Another scale finding significant utility is the Lscale representing the mantissa of the common logarithm (base 10) of anumber on the C or-D scale; hence the L scale represents thevalue log Xand is decimally subdivided along the rule, whereas each of the otherscales mentioned earlier is logarithmically subdivided. It is also notuncommon to provide a P scale of the Pythagorean relationship l X scalesfor the trigonometric functions sine, cosine, tangent or cotangent in60-division (sexagesimal) units or other wise, and so-called log-logscales LL01, LL], LL02, LL2, LL03, LL3 representing positive andnegative exponents of the natural logarithm base e.

In addition, the specialized scales may be provided for certainmathematical, technical, commercial, banking or financial purposes, oreven for the more specialized subjects of science and technology, namelyelectrical technology, mechanical engineering, chemistry, reinforcedconcrete, printing topographical activities, telecommunication,automotive racing, navigation and aeronautics.

OBJECTS OF THE INVENTION It is the principal object of the presentinvention to provide an improvedslide rule with some or all of theconventional scales previously described, but with in- SUMMARY OF THEINVENTION These objects and others which will become apparenthereinafter are attained, in accordance with the present invention, witha circular or elongated'(linear) slide rule having the usual rule bodywith at least one scale face, a slide received in this body andshiftable relatively thereto while being provided with a slide facesubstantially coplanar with the scale face of the rule body, and acursor provided with a reticle or hairline adapted to sweep across thefaces, the body face being provided with at least the A and D scalesmentioned earlier while the slide is provided with at least the B and Cscales such that the scales extend across the entire effective length ofthe rule and have alignable indices or origins at least at one portionof the scale and preferably at the left-hand end thereof when the scaleis of the linear type. I have found that the versatility of such a scalemay be markedly increased for almost general applicability, by providingit with a further scale represented as BF and constituting a folded"form of the B scale offset from the common B scale by the value 1r. Inother words, the BF scale has the index 1r and, as illustrated, withlogarithmic subdivision disposed in line with the indices 1 (theorigins) of the A, B, C and D scales, at least in the normal position ofthe slide. The

BF scale, according to the present invention, is provided upon the slidefor co-operation with the X scales A and B or with the X scales C and D,and itself'represents the value 1rX However, the BF scale does notextend over the full length of the other scales, but terminates at anumerical value of about 36 so that beyond the BF scale and in linetherewith I provide a further calculating scale, e.g. a scale [C ofcentesimal trigonometric values.

It has also been found to be advantageous in conjunction with the use ofprovision of the BF scale, to supply certain indices, marks orhighlighted points to facilitate calculation. For example, I provide anindex W to indicate the value 2.17 on the basic scales C and D to allowthe diameters of full circular sections to be set rapidly and allowing adirect reading on the cube scale K of the .axial resistance modulus ofbending. Conversely, using this index, one can calculate the diameter ofthe section by introducing the value of the modulus at the K scale.

Still another feature of the invention resides in the provision of anindex W on the basic C and D scales, or one of them (proferably the Cscale) to indicate the value l.72 thereby allowing the diameter of solidcircular sections to be set on the K scale and the polar resistancemodulus to be directly read out.

DESCRIPTION OF THE DRAWING The above and other objects, features andadvantages of the present invention will become more readily apparentfrom the following description reference being made to the accompanyingdrawing in which:

FIG. 1 is a plan view of the slide rule of the present invention as seenalong its face;

FIG. 2 is a longitudinal side view thereof; and

FIG. 3 is an elevational view of the slider removed from the rule.

SPECIFIC DESCRIPTION In FIGS. 1 3, I show a slide rule which comprises abody A, a slide B and a slider or cursor C, all of which can be shiftedlongitudinally relative to one another. The rule body A comprises a woodcore of trapezoidal cross section having an inclined flannk 100, aperpendicular flank 101, a rear face 102 and an upper surface 103. Thechannel 104 is provided with walls in which the tongues 105 of the slideB are received. Appropriate grooves are also provided to guide thecursor C which has a hairline or reticle 106. The body is faced .June21, 1971, this scale can be constituted as an L scale for indicatingmantissae of the common logarithms ofa number selected on the C or Dscale, or for allowing the number to be determined when thema'ntissa isknown. Along the upper edge of the face of the rule body A, l'provide ascale P of the pythagorean values ll X and below the scale, the scale Kof cubic values X" designated at 3. A scale 4 is located along the loweredge of the upper strip of the face of the scale body and constitutesthe basic square scale A representing the value X Along the upper borderof the lower strip of the scale body, there is provided the base-value Dscale at 10 such that a number selected onthe D scale corresponds to thesquare of this number on the A scale. A scale 11 directly below the Dscale represents LLl and the value e and is followed by scale 12 and 13corresponding to LL2 and LL3 and representing the values e-"" and e-".Along the right-angle flank of the rule body, there is provided at 17 ascale R establishing the ratio 1:25 and the purpose of which will beapparent hereinafter. Above the scale, on the edge of the rule body,there is provided the decimally subdivided scale 16 corresponding to aconventional L scale and representing the mantissa of the values log X.

The slide is provided along its upper edge with a square scale Bidentical in all respects with the scale A and indicating the value Xwhen the hairline 106 is applied to a value X on the C scale discussedin detail hereinafter. Scale B is designated by the reference numeral 5.Similarly, along the lower edge of one face of the slide B, I providethe base-value C scale which corresponds identically to the scale D andcooperates therewith for ordinary multiplication and division. Thisscale 9 indicates the value X. Immediately above the latter scale is aninverted or reciprocal scale CI corresponding to the reciprocal of the Cscale multiplied by 10 and therefore representing the ratio lOzX, thisscale being designated at 8.

According to the present invention, a scale 6 is provided in the form ofa folded B scale represented by the designation BF and with an originset at 11' and extending to the value 36 or at least to the value 10wsuch that this scale represents the product rrX for a number X indicatedon the C scale number X of the B scale (see example 7 (a) infra). Sincethis scale BF only extends over a portion of the length of the slide B,the balance is provided'with a scale 7 (IC) representing centesimaltrigono-metric scales having a black portion representing arc sine orare cosine and a red inverse section representing the arc tangent or arccotangent.

Along thereverse side of the slider B are provided trigonometric scalesincluding a scale S, of the sexagesimal trigonometric arc sines and arecosines in terms of sine 0. l X and cosine 0. IX for large angles, ascale designated ST of the arc sines, arc tangents and angles of are forvalues corresponding to 0.0lX and a scale T, for the sexagesimaltrigonometric arc tangents or are cotangents (tangent 0.1X, contangent0.1X) for large angles.

In the floor of the channel 104 in which the slider is received, Iprovide scales 14 and 15, the first being a doubly colored scale ofefficiencies such that the black left-hand'side is marked PINAM toindicate the efficiency of electromagnetic dynamos, while a red scale onthe right-hand side is marked ELMOT representing the efficiency ofelectric motors. The DINAM scale extends between 1 20% and n while thereciprocal ELMOT scale runs from n 100% to 17 20%. The lower scale 15 onthe floor of the scale is represented as a AU-scale of voltage dropsubdivided between 0.5 and 10 volts.

To facilitate use of the device, various indices are marked on the ruleincluding the following:

a. the right-hand and left-hand indices 1 of the basic C and Dscaleswhich correspond or are aligned with the indices 1 of the A and Bscales, the index 10 of the b. lndices W, and W newly applied accordingto the invention and representing the value 2.17 and 1.72 on the C scaleas already described. These scales are described in greater detailbelow. W, 1rd /32 (d/2.l7) E 2.17 W,,= ad /16 =(d/1.72) E 1.72 l c. Anindex c on the C scale of the slide B at the point corresponding to thevalue of they V 4/11'.

e. lndices p, p, p"and p on the slide scale C representing the radianvalues 180/ p X 57.32, (180 60)/1r 3437.7, (180 X 60)/1r 206264.81 and200/11 f. An index L on the scale C marked at the value log e 2.303. i l

g. lndices 1r for the scales A, B, BF, C, Cl and D marked at thevalue.3.l416 thereof.

h. An index Cu based upon the relationship R =p X 1/A marked on the Ascale and corresponding to the value 1.785. This indexallows-calculation of electrical resistance of copper conductors with afull circular cross section.

i. An index Cu marked in red on the scale A, to contrast with the blackscale discussed immediately at (h) and based upon the relationship G y Xl X A. This mark, at the value value 1 1.22 facilitates calculation ofthe weight of a copper conductor of solid cross section.

j. lndices 736 on the scales A and B representing the ratio ofhorsepower to kilowatts (0.736).

k. An index M on the B scale representing the value 100/1r 31.831.

1. lndices 287 on scales A and B representing the value 28.7corresponding to half the cond'uctivity of copper.

nential LL3 and at the end of exponential scale LL2.

0. An index q on the cursor C adapted to ride along scale A and markedto the left of the reticle 106 at a distance therefrom 4/11' 1.1284corresponding to the scale of square values.

p. lndices KW located at the hairline and a location offset therefrom bya distance which will be described hereinafter, the hairline index KWbeing disposed at the scaleA while 'the offset index KW is disposedalong the D scale.

q. Two indices CP on the right-hand side of the window of the cursoradapted to ride along scale A and scale D respectively and correspondingto the relationships HP/0.736 and l-lP/l .35964 on these scales asmeasured from the hairline. The hairline for the index HP at the levelof scale D is marked to the right of the hairline-by a distance equal tothat of the index q to the left thereof.

r. An index SEXA on the cursor to the left of the hairline with an indexmark lying along scale D and at,

t. An index don the cursor reading along the D scale.

The reverse side of the rule body is provided with ta-' bles D of-dataand engineering and technical constants.

OPERATION a. In order to find the perimeter of a circle with thediameter d= 1.4 m the hairline of the cursor is set on' the division ofthe scale of squares B of the slider and, along the same hairline,beneath, at the scale BF the perimeter 4.398 m may be read, without anycalculations or movement anew of the cursor or the slider.

b. 1n order to find the diameter of a circle with the perimeter p 6.6the'hairline of the cursor is fixed at the division 6.6 on the scale BF,and the diameter 2.108 m may be read directly at the same hairline onthe scale B of the slider. c. In order to find the value of 1rd when d12 cm, the hairline of the cursor is fixed on the basic scale C of theslider at the division 12, and at the same hairline, 'on the scale BFthe result 452.4 cm may be read, without any calculation or displacementof the slider.

rectly on the scale BF without any calculation.

e. Many values for quantities expressed in units in the composition ofwhich are the time-second, the sexagesimal degree-second, the dayapproximated as the -3 60th part of a year can be converted in a simpleway into. values in such units as hours, sexagesimal degree, years andvice-versa. The same counts for other conversions, in which the ratio1:36 or its inverse appears, which are frequent in physics and intechnology. For such transformations the slider is moved to the left,bringing the end division 36 of the BF scale against the division 10 ofthe scale A; the given values and those sought are face-tmface on thesescales and the results are obtained without any calculations, only bymoving the cursor."

f. In order to transform 0.25 kWh into .loules, the reticle of thecursor is set on the scale A at the division 25 and below it on thescale BF at the hairline the value 9 is directly read; the result is900,000 Joule.

g. To transform 5.2 into sexagesimal seconds, the hairline of the cursoris set along the scale A the division 5.2 and beneath, on the scale BFof the slider, at the hairline the value 1,872 is directly read; theresult is 18,720 I h. To express 1.5 hours in seconds, the hairline ofthe cursor is set on the scale A at the division 1.5 and beneath, on thescale BF of the slider at the hairline, the

value 5.4 is directly read; the result is 5,400 seconds.

i. In order to express 21 days in years, the hairline of the cursor, isset on the scale BF of the slider at the division 21, and above, on thescale A, at the hairline, 583

'is directly read, the result being 0.0583 year.

k. To find the number of Ohms constituting the capacitive reactanceof analternating current with a frequency of SOl-lz, having a capacitance of1.l5p.F, the hairline of the cursor is set on the basic inverse redscale CI of the slider at the division 1.15 and beneath, on scale C ofthe slider an intermediate value 8.7 'is read; moving the cursor to theleft, the division 8.7 is set with the hairline on the scale BF, anddirectly above, at the hairline on the scale B, the value 277 is read;the result is 0.00002770.

l. A way to resolve the former Example (k) in the particular case inwhich the frequency is different from 50Hz is as follows: In order todetermine the number of Ohms constituting the capacitive reactance ofanalternating current with a frequency of 60l-lz having a capacitance ofl.lp.F, the hairline of the cursor is set on the basic red inverse scaleCl at the division 1.15; beneath, on the basic scale C, an intermediatevalue 8.7 is read at the hairline; moving the cursor to the left, on thescale A the division 120 is fixed, representing the double frequency inHz; the slider is then pushed to the left, bringing the division 8.7 ofthe scale BF to the hairline, and at the beginning of the division, 1,of the square-scale A; on the scale B of the slider the value 231 isread; the result is 000002319.

m. In order to determine the pulsation resonance of an alternatingelectric current circuit containing an inductance of 200ml-l and acapacitance of 380 uF, the procedure is as follows:

On the scale A is set at the division 380 (representing the value of thecapacitance) the origin index 1 of the scale B; then the hairline of theslider is set on the division 200 (representing the value of theinductance) of the scale B; then, moving the slider to the left, thedivision 2 of the basic red inverse scale Cl is brought to the on thebasic scale D of the body, at the index W the hairline of the cursor. Atthe origin index 1 of the basic scale C the intermediate value 174 isread on the basic scale D, which is set with the hairline of the cursor;moving the slider to the left, that intermediate value 174 on the BFscale is brought to the hairline and into line with the origin index 1of the scale A, on the scale B the final result of l8.25 periods persecond (Hz) is read, which is the resonance pulsation sought.

n. In order to find the axial modulus of resistance to bending W, of adriving shaft with full circular section having a diameter ofd= 5cm, theindex W, of the basic scale C is placed on the division 5 of the basicscale D of the body; then the cursor is brought with its hairline on theorigin division I of the slider, and above, on the cube scale K theresult l2.27cm is read at the hairline.

0. ln order to find the necessary diameter of the circular full sectioncorresponding to the known axial modulus of resistance to bending W,l2.27cm the hairline of the cursoris set on the cube scale K at thedivision 1227, whereupon the origin index 1 of the slider scale C isbrought to the hairline, and, on the basic scale D of the body, at theindex W the result d 5cm is read.

p. In order to find the polar resistance modulus W of a shaft with afull circular section having a diameter of d 3cm, the division 3 ofthe'basic scale D of the body is set with index W,, of the basic scaleC; then the hairline of the cursor is brought over the origin index l ofthe C scale, and above, on the scale K of the cubes, the result 5.3cm"is read on the hairline.

q. In order to find the necessary diameter for the circular full sectioncorresponding to the known polar resistance modulus W, 5.3cm thedivision 5.3 isset on scale K, with the hairline of the cursor; then,theorigin division 1 of the slider is brought to the hairline, and

result d 3cm is read.

The slide rule for general purposes, provided with the new scale BF ofthe squares displaced by 1r and with the nes indexes W and W accordingto the invention, offers the following advantages of increasedefficiency of utilization:

The scale BF, offset by 11', complete or limited to the value of 36simplifies in a substantial way the calculations with 1r, a constantoutstandingly frequent in physics, mechanics, machine construction andelectrotechnic values; the scale permits simple determination of theperimeter of the circle for a known diameter and vice-versa, simplifiesthe resolving of relations of the form 1rd the calculation of theinductive and capacitive reactance, calculation of the resonancepulsation of alternating electric circuits, and also a large number oftransformations and conversions frequent in science and technology.

The indexes W, and W, on the basic scale of the slider is interestingfor calculations of the resistance of materials, obtaining directly,easily the axial and the polar resistance moduli ofthe solid circularsections for any given diameter and vice versa, for direct calculationof the diameter when one of these moduli is given as necessary. Thesenew fixed marks are outstandingly useful for calculating sizes whendesigning all kinds of machines or reinforced-concrete structures withround bars, as well as to check design calculations in these fields.

The slide rule of the invention example brings also a number of otheradvantages. Thus, placing the exponential scales for e e and e upon theupper face of the slide rule, precise locating and reading of the scalesby means of the semicylindrical magnifying glass of the cursor; thisfacilitates the extraction of roots of any order, raising a number toany power, either positive or negative, and simplifies direct andprecise reading of the result. Also, many superior intricatecalculations can be made using the exponential scales combined with therest of the scales of the obverse face of the slide rule, in order toreduce the great volume of calculations frequent in the field ofelectrotechnology, chemistry and nuclear physics. The indices CENTE andSEXA on the cursor allow direct reading in centesimal degrees of anyangle shown in sexagesimal degrees and vice versa without calculations,combined with the possibilities given by the scale 1c of the centesimaltrigonometric indices.

I claim:

1. A slide rule having a body provided with a scale face, a slideshiftable relatively to said body and provided with a slide face, and acursor having a hairline adapted to sweep across said scale faces, afirst basevalue scale D with the functional notation X subdivided andprovided on said scale face, a second base-value scale C with thefunctional notation X corresponding to the first base-value scale andformed along said slide face, said base-value scales C and D cooperatingwith said hairline to indicate a value X, a first logarithmicallydivided square scale A formed on said scale face and indicating thevalue of X for a value X selected by said hairline on said first-valuescale, a second logarithmically divided square scale B formed onsaidslide face and indicating the value X for a value X selected by tionalnotation 1rX and having an origin ocrresponding to the value ii-alongwith the origins of said first and second square scales and said firstand second base-value scales, said folded square scale BF indicating theproduct 'n'X? for a value X selected by said hairline on said secondbase-value scale, an index W, formed on said second base-value scale atthe value 2.17 thereof, and an index W along said second base-valuescale at the value 1.72 thereof, said indices W, and W being provided onthe slider.

2. The slide rule defined in claim 1 wherein said BF scale is disposedbetween said B and said C scales for co-operating with said A and Dscales.

3. The slide rule defined in claim 2 wherein said BF scale has a lengthless than the full length of said slider face, said slide rule furthercomprising a trigonometric centesimal scale in line with said BF scaleand extending over at least part of the remainder of the length of saidslider face.

4. The slide rule defined in claim 3 wherein said BF scale terminates ata value of approximately 36.

5. The slide rule defined in claim 4, further comprising an L scaleformed along said body and decimally subdivided with an origin alignedwith the origin of said D scale, a P scale formed along said body andindicating the value I l X for a value X indicated by said hairline onsaid D scale, a logarithmically divided scale K formed on said body andindicating the value X for a value X indicated by said hairline alongsaid D scale and at least one sexagesimal trigonometric scale formedalong said slider and indicating a trigonometric function inco-operation with said C and D scales.

6. The slide rule defined in claim 5 wherein said channel has a floor,further comprising at least one scale formed along said floor forindicating efficiency of electric machines and at least one scale alongsaid floor for indicating potential drop.

7. The slide rule defined in claim 6 wherein said scale face is providedwith at least one scale representing a value proportional to e where Xis a value selected by said hairline along the D scale.

8. The slide rule defined in claim 7, further comprising a set ofco-operating indices on said A and B scale and on said cursor forfacilitating power calculations. =l

1. A slide rule having a body provided with a scale face, a slideshiftable relatively to said body and provided with a slide face, and acursor having a hairline adapted to sweep across said scale faces, afirst base-value scale D with the functional notation X subdivided andprovided on said scale face, a second base-value scale C with thefunctional notation X corresponding to the first base-value scale andformed along said slide face, said base-value scales C and D cooperatingwith said hairline to indicate a value X, a first logarithmicallydivided square scale A formed on said scale face and indicating thevalue of X2 for a value X selected by said hairline on said first-valuescale, a second logarithmically divided square scale B formed on saidslide face and indicating the value X2 for a value X selected by saidhairline on said second base-value scale, a folded logarithmicallydivided square scale BF with a functional notation pi X2 and having anorigin corresponding to the value pi along with the origins of saidfirst and second square scales and said first and second base-valuescales, said folded square scale BF indicating the product pi X2 for avalue X selected by said hairline on said second base-value scale, anindex Wz formed on said second base-value scale at the value 2.17thereof, and an index Wp along said second base-value scale at the value1.72 thereof, said indices W, and Wz being provided on the slider. 2.The slide rule defined in claim 1 wherein said BF scale is disposedbetween said B and said C scales for co-operating with said A and Dscales.
 3. The slide rule defined in claim 2 wherein said BF scale has alength less than the full length of said slider face, said slide rulefurther comprising a trigonometric centesimal scale in line with said BFscale and extending over at least part of the remainder of the length ofsaid slider face.
 4. The slide rule defined in claim 3 wherein said BFscale terminates at a value of approximately
 36. 5. The slide ruledefined in claim 4, further comprising an L scale formed along said bodyand decimally subdivided with an origin aligned with the origin of saidD scale, a P scale formed along said body and indicating the valueSquare Root 1 - X2 for a value X indicated by said hairline on said Dscale, a logarithmically divided scale K formed on said body andindicating the value X3 for a value X indicated by said hairline alongsaid D scale and at least one sexagesimal trigonometric scale formedalong said slider and indicating a trigonometric function inco-operation with said C and D scales.
 6. The slide rule defined inclaim 5 wherein said channel has a floor, further comprising at leastone scale formed along said floor for indicating efficiency of electricmachines and at least one scale along said floor for indicatingpotential drop.
 7. The slide rule defined in claim 6 wherein said scaleface is provided with at least one scale representing a valueproportional to eX where X is a value selected by said hairline alongthe D scale.
 8. The slide rule defined in claim 7, further comprising aset of co-operating indices on said A and B scale and on said cursor forfacilitating power calculations.